The present invention relates generally to heating ventilation and air conditioning (HVAC) systems, and, more particularly to an air temperature sensor for an automatically controlled HVAC system.
Automatic control of HVAC systems requires that the correct temperature of air flowing through the air ducts and outlets be determined. An electronic sensor, installed in an air duct, produces a signal representing the temperature of air flowing in an air duct. The sensor includes a NTC thermistor and two leads coated with epoxy, housed in a plastic body.
It is conventional to form HVAC air ducts by a blow molding process that causes the thickness of the duct walls to vary from 0.70 mm. to 2.25 mm. A conventional sensor assembly includes a plastic retainer having two ribs spaced about 1.5 mm. apart, which ribs engage the duct wall when the sensor assembly is inserted into the duct. A temperature probe portion of the assembly is inserted in the retainer and held in position on the duct wall. Terminals of the sensor assembly are then connected by a wiring harness to an electronic HVAC control module.
The retainer's ribs cannot accommodate or compensate for variations in the thickness of the duct, if the duct wall thickness varies much from 1.5 mm. Additionally, the temperature sensor is sensitive to variations in the diameter of the hole formed in the duct wall where the sensor is located. Consequently a sensor, poorly fitted in the duct wall, can lose its retention on the duct wall, disengage and become lost at a vehicle assembly plant.